This invention relates generally to a method and apparatus for constructing a drainage device or system for use in removing water either on a hillside, in the vicinity of foundations or the like, or in filtration systems.
In order to maintain basement interiors dry and moisture free, it is necessary to remove water penetrating the soil mass adjacent the subterranean walls quickly, while avoiding a decrease in the strength of the soil "piping" or pore pressure. Such removal is often accomplished by means of drainage systems comprising drainage pipes surrounded by a mineral aggregate. The particle size distribution of the aggregate must be carefully matched to the native soil in the region of construction. The functions of a properly designed drainage system are to remove water from the surrounding soil while "filtering" preventing movement of soil particles therefrom. Many of the prior art drainage systems as discussed hereinabove suffer from significant deficiencies and disadvantages caused by clogging or other malfunctioning.
U.S. Pat. Nos. 3,563,038, 3,654,765 and 4,490,072 (all three prior patents being fully incorporated herein by reference) overcome the significant problems of prior art drainage systems by disclosing drainage devices of the type which include a drainage pipe provided below a core surrounded by a ground water pervious material to provide a pathway for the water through the core into the drainage pipe. The drainage device disclosed in these three patents are well known by the terms subterranean wall drain, drainage system or composite curtain drain. Drainage systems of this type are commercially marketed by the ELJEN CORPORATION of Storrs, Conn. Typically, this drainage system comprises an envelope of a nonwoven filter material having a core which leads to a pipe inside the water pervious nonwoven material. This core comprises a plastic sheet having a plurality of alternate valleys and raised portions defined in the sheet. Preferably, this core leads to a slotted pipe. During use, water enters the pervious envelope material, flows downwardly along the corrugated hills and valleys of the plastic core material and then enters into the slotted pipe to be carried away from the hillside, foundation or filtration system. Thus, as so constructed, the drainage device of the prior patents are well adapted to handle the downward flow of water beneath the surface of the ground in a drainage system or a septic system filter such that normal hydrostatic pressure will force this water inwardly through the water permeable filter material and into the valleys defined in the core where gravity carries the water downwardly to the drainage pipe and more particularly to the slotted openings in the drainage pipe.
Previously, several different methods and devices have been used to produce the drainage system described in the above cited patents. Significantly, all of these methods for producing the drainage system relate to a continuous process for producing only the plastic core (containing the hills and valleys). It will be appreciated that subsequent to the production of the core, the water permeable fabric is cut and sewn into a cloth envelope whereupon the core and slotted pipe is inserted therein either at the plant or on the job site. Two distinct types of methods have been used in forming the core. One method involves the use of a vacuum forming machine which consists of a flat steel mold for producing the desired shape with small holes where a vacuum is applied. It will be appreciated that the vacuum pulls down the plastic sheet to the mold surface to form the desired bumps and valleys. This vacuum forming-type device also includes a heat chamber where the plastic is heated prior to being pulled over the forming die. A second method of forming the plastic core is by using a pressure forming machine which also utilizes a heat chamber where plastic is heated and softened and then pulled over or through a die set whereupon the hills and valleys are formed between two die surface. These surfaces are matched dies which can be either flat or in the form of rollers.
Such a pressure forming machine as described above has been used by Trans World Consulting Co. Inc. of Windsor Locks, Conn., and comprises a heat chamber where preferably radiant heaters are applied to soften a continuous plastic sheet. Other types of heaters or heating units such as infrared, wire, cartridge, microwave, gas, or the like could also be used in the heat chamber to heat the plastic. In this pressure forming machine, two pressure forming rolls have been applied to form the "butts" i.e., raised hills or valleys into the previously heated and softened plastic sheet. The pressure forming rolls consist of a pair of mandrels having round pins of approximately 11/2 inches which are pressed or threaded into each mandrel. Of course, any shape pin may be used to form the hills and valleys such as a square, hex, octagonal or any other shape so long as the plastic core material is provided with a corrugated, uneven surface having raised portions and lower portions.
While suited for its intended purposes, the apparatus and method of making the drainage system of the aforementioned patents suffers from several inefficiencies and drawbacks. For example, as mentioned, while the plastic core is being formed by the pressure forming machine, the water permeable fabric must be cut and sewn to form an envelope which will receive the core material. Thereafter, after the core has been stuffed into the envelope, further sewing steps may be needed to enclose the core. The necessity for prefabricating the cloth envelope along with the subsequent labor steps of stuffing the core material into the envelope is labor intensive, expensive and time consuming. Moreover, from a practical manufacturing standpoint, the separate labor steps needed to prefabricate and stuff the envelope dramatically decreases the daily output of the drainage system thereby adding to costs and limiting sales.